Yesterday, Japan's Fisheries Agency said the whaling program had been put on hold because of harassment by Sea Shepherd activists.

"We are now studying the situation, including the possibility of cutting the mission early," agency official Tatsuya Nakaoku said, confirming media reports, but stressing that "nothing has been decided at this point".

But Mr Watson, who is on board the Sea Shepherd ship Steve Irwin in the Ross Sea, says it is unclear what the whaling fleet, led by the Nisshin Maru processing ship, is doing.

"The boats enter the Drake Passage to go into the Southern Atlantic Ocean," he said.

"This morning they suddenly turned around, did an about face, and now they are coming west again.

"We don't know if that means they are on a great circle route back to Japan or they are returning to the whaling grounds.

"The harpoon vessels remain in the Ross Sea and we intend to stay here until they leave.

"We don't know if this suspension is permanent. Two weeks or two days, we don't know.

"It could be a ploy but all indications are that yes they are going home but we don't know that for an absolute certainty," he said.

"We had planned to be here until the end of March, the end of whaling season but we don't know."

Greens Leader Senator Bob Brown says it will be at least five days before it is known whether the Japanese fleet is heading back home or to other whaling grounds.

"But they're in serious disarray. They've been able to get less than 100 whales when they were aiming to get 940 this season," he said.

"That's financially disastrous and as Paul Watson's always said, ultimately what will bring them home and bring them down is the inability to pay the hundreds of millions of dollars loans they have from the Japanese government."

Sea Shepherd activists have harassed whalers in recent years, moving their ships and inflatable boats between the harpoon vessels and whales and throwing stink and paint bombs at the whaling ships.

And Sea Shepherd says the strategy of placing vessels in the slipway of the processing ships has severely hampered the whaling outfit this year.